If you're not too competitive about it, then even a single player can have an impact in GvG. I only dabble, I play on mobile most of the time, but I'll dip into a lower era map or two where I still have lots of troops every few months and take some sectors. But going overboard can be a problem, the number of guild goods required goes up with each sector held. Last time, I wasn't paying attention and went farther than I should have on one map and needed to do some trades to add back to the guild treasury.